Lan Leased Time

It is recommended that I should set the leased time to forever for a
Home Network.

What would happen if I set it to a smaller value, like 1 hour ? What
would happen to the network clients ?

I'm seeing that the HostNames of PC are still appearing on my DHCP
Client Log even after they go away. Would it help if I set the Leased
Time to half hour ?

Thanks.

Probably nothing special would happen. Your machine would simply update
the same IP address as before without you noticing a thing.

But example in my case, my IP webcam stopped working properly. My ISP
leased a IP for 3 hours at time and as result my camera worked 3 hours
and then jammed. No idea why this D-link DCS-5300W can´t update the
leased IP, but works just fine with NAT.

As for your log question, I suggest you try it and report back

I've change it. Seems ok but it does not mean it's OK, right ?

And I'm referring to the Lan, not WAN in your case.

Thanks.

On 29 Jul 2005 23:59:36 -0700, (E-Mail Removed) wrote:

>It is recommended that I should set the leased time to forever for a
>Home Network.

Dumb idea. No benifit. If you're running an open access point, with
no encryption, every passing laptop will grab an IP address, and hold
it forever. Eventually, you'll run out of IP addresses. This is
exactly what happens at many coffee shop hot spots that use too long a
lease time. If you're running a close and encrypted system, you're
unlikely to have this problem.

>What would happen if I set it to a smaller value, like 1 hour ? What
>would happen to the network clients ?

Nothing. The Windoze algorithm for renewing the lease is to request a
renewal at half the lease time. So, if you issue a 1 hr lease,
Windoze will request a renewal after 30 mins. If it doesn't get it,
it will pound on the DHCP server roughly every 12 minutes until it
expires.

>I'm seeing that the HostNames of PC are still appearing on my DHCP
>Client Log even after they go away. Would it help if I set the Leased
>Time to half hour ?

I don't think you can set it to 1/2 hour. Most cheapo routers have 1
hour as the minimum. Since you didn't bother disclosing what router
make and model you own, I can verify if this is true for your device.

So, what problem are you trying to solve? If you just want to retain
a MAC address to IP address mapping, just use the "static DHCP"
feature found in many routers. In effect, it's an infinitely long
lease time that doesn't screw up badly if the power is cycled and the
leases are lost.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# http://802.11junk.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

Jeff Liebermann wrote:

> Nothing. The Windoze algorithm for renewing the lease is to request a
> renewal at half the lease time. So, if you issue a 1 hr lease,
> Windoze will request a renewal after 30 mins. If it doesn't get it,
> it will pound on the DHCP server roughly every 12 minutes until it
> expires.

I'm also using Pocket PC with Windows Mobile 2004 2nd Edition. Would
this apply ?

> So, what problem are you trying to solve? If you just want to retain
> a MAC address to IP address mapping, just use the "static DHCP"
> feature found in many routers. In effect, it's an infinitely long
> lease time that doesn't screw up badly if the power is cycled and the
> leases are lost.

1. I want the client not to be showing up on the router anymore. When
a client connects to the router and then goes away, the MAC still shows
up on the router.

2. I don't know if this is related. My PDA connects wirelessly to the
router. Sometimes, esp overnight, it cannot connect. I have to reboot
the router.

On 2 Aug 2005 03:06:09 -0700, (E-Mail Removed) wrote:

>
>Jeff Liebermann wrote:
>
>> Nothing. The Windoze algorithm for renewing the lease is to request a
>> renewal at half the lease time. So, if you issue a 1 hr lease,
>> Windoze will request a renewal after 30 mins. If it doesn't get it,
>> it will pound on the DHCP server roughly every 12 minutes until it
>> expires.

>I'm also using Pocket PC with Windows Mobile 2004 2nd Edition. Would
>this apply ?

Renewal at 50% of lease time is standard for all DHCP clients.

Drivel: Where it gets really long is the Windoze WINS (NETBIOS to IP)
renewal and extinction interval. The default times are:
Renewal interval: 144 hrs (6 days)
Extinction interval: 144 hrs
Extinction timeout: 144 hrs
Verify interval: 576 hrs (24 days)
However, that's not the problem here.

For DHCP it's the clients responsibility to initiate renewals and the
servers responsibility to know when to expire the lease. This article
discusses how it works, and makes specific recommendations against
ultra long DHCP lease time:
http://www.windowsitlibrary.com/Content/155/08/1.html#1
Apparently if the DHCP server goes offline for some reason, when the
clients notice that 7/8th of the lease time has arrived without a
renewal acknowledgment, they start spewing multiple DHCP discover
messages (rebinding) trying to find another DHCP server. It probably
won't generate any noticeable increase in traffic on a small network,
but it's really ugly when it happens at a large ISP.

More detail on DHCP (3 pages):
| http://www.tcpipguide.com/free/t_DHC...gProcesses.htm

If you want to play, try this free DHCP query tool:
| http://www.weirdsolutions.com/weirdS...ytool_free.exe

>1. I want the client not to be showing up on the router anymore. When
>a client connects to the router and then goes away, the MAC still shows
>up on the router.

Well, then shorten the router DHCP lease time to the minimum, which
usually 1 hour. If the client disappears, it will disappear from the
list within 90 minutes. Is that short enough? If you want shorter
lease times, you'll have to hack the firmware or use an external DHCP
server. I had to do that with busy system that was filling up the
DHCP table far to rapidly, leaving no slots for additional clients.
We were delivering routeable addresses (bad idea) so the available
number of IP's was very limited.

I had a friend do some tweaking and set it up so that any DHCP renewal
request always returns a negative acknowledgement at rebinding time.
That would instantly expire the lease at the server at rebinding time
and flush the table entry. No waiting for a timeout. The client
would then search for a new DHCP server and get a new lease. That
worked fairly well, but is rather nonstandard. It also had the
side-effect of changing the IP address of all the users if all the
leases were issued. Eventually, we gave up and just left it at 15
minute leases.

>2. I don't know if this is related. My PDA connects wirelessly to the
>router. Sometimes, esp overnight, it cannot connect. I have to reboot
>the router.

I haven't the slightest idea, especially since you didn't supply the
make and model of the your router, your PDA, and any troubleshooting
that you've done. However, I can speculate that if you turn off the
PDA at night, and your router still has your PDA's MAC address in the
DHCP table, it should reconnect exactly where it left off the night
before. I do that on my own systems and find that I get the same IP
address for days on end. Look at the IP status screen on the PDA and
your unspecified routers log file page for any error messages.



--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
AE6KS 831-336-2558